The present invention relates to compression molding technology and in particular to a cam operated mechanism for operating a compression molding apparatus. In a compression molding apparatus, a female mold cavity receives a quantity or charge of moldable thermoplastic material, and a male plunger compresses the thermoplastic material within the female mold cavity to create the desired shape. The present invention provides a cam operated mechanism which, in response to axial movement between the female mold cavity and the male plunger, causes a side movement or lateral separation of a portion of the female mold cavity to allow removal of the compression molded article.
Existing compression molding machines are used for producing articles such as closures for bottled liquids. In a rotary-type compression molding machine, a plurality of compression mold assemblies are arranged around a rotating carousel. Each assembly includes a mold formed by a male mold half (or xe2x80x9cforming pinxe2x80x9d) and a cooperating female mold half (or xe2x80x9ccavityxe2x80x9d) which are reciprocally, vertically opened and closed together to form compression molded articles such as bottle closures or caps. The mold halves are separated vertically or xe2x80x9copenedxe2x80x9d to receive a charge of molten plastic, and mated together vertically or xe2x80x9cclosedxe2x80x9d to form the compression molded article. The halves are then separated and the article removed in a substantially vertical direction from one of the mold halves, such as by removal from the male mold forming pin. These steps occur progressively as the assemblies are circulated with the rotating carousel. These compression molded articles were heretofore limited to articles having shapes which could be removed from one of the mold halves in a direction parallel to a direction of separation of the mold halves.
As an example, bottle closures, such as threaded bottle caps, typically have inside threads. Once compression molded, the cap must be either unscrewed from the male mold half or stripped (forcibly removed in a non-rotary manner) from the male mold half to remove the closure. Typically, stripping can be successfully accomplished without unacceptable thread damage because the molded article is sufficiently thin-walled and flexible to be removed from the male mold half. U.S. Pat. No. 4,497,765, hereby incorporated by reference, describes compression molding of a bottle closure.
Although bottle caps with inside threads are effectively compression molded, other products having a more complex shape are difficult or impossible to remove after compression molding by simple separation of the male and female halves. External threads, for example, such as used on a bottle neck, are more difficult to strip or unscrew from within a female mold half. Unscrewing the completed article from the mold half requires more complex machinery and requires machine operating time, i.e., machine throughput is decreased. Also, articles molded of particularly rigid plastic material, or articles having thick walls, are sometimes difficult to strip from the male or female compression mold halves without damage to the articles.
It would be desirable to provide a mechanism for a compression molding apparatus which facilitated the removal of molded articles from the compression molding apparatus and which eliminated the requirement for stripping or unscrewing threaded articles from the mold.
In order to produce complex products like tamper evident closures with molded-in bridges, articles with holes in the radial direction, or articles with external threads, the compression mold of the present invention has a mold portion with the capability for side or lateral movement to open up the mold in a lateral direction after molding, to remove the molded article.
The invention contemplates a compression mold assembly which includes a mold formed between a relatively reciprocating male mold plunger and a female mold cavity, wherein a portion of a wall which at least partly defines the female mold cavity is movable in a lateral direction after molding, to allow removal of the molded article. The embodiments of the invention include a cam mechanism for actuating mold xe2x80x9cside pullsxe2x80x9d or levers to laterally disengage or separate the molded article from the female mold cavity in order to axially remove or eject articles from the compression molding machine. The use of cam mechanisms to provide lateral movement or xe2x80x9cside actionsxe2x80x9d of a mold portion, activated by the relatively reciprocating male and female mold halves, is believed to be heretofore unknown in compression molding machines.
The present invention contemplates a cam mechanism for a compression molding apparatus having a mold formed by cooperating male and female mold halves and a slide mold part. The male and female mold halves are relatively reciprocated vertically toward and away from each other. The slide mold part is held relatively stationary in a vertical direction with the male mold half, and forms a female mold cavity together with the female mold half. The female mold cavity receives a male plunger of the male mold half to form an article in the space defined between the plunger and the female mold cavity.
The male and female mold halves are reciprocated vertically to sequentially receive a charge of moldable plastic, compress the moldable plastic into a shaped, compression molded article, and then separate to allow removal of the article from the mold. The cam mechanism interacts with at least one male or female compression mold half, or both male and female mold halves, to separate the slide mold part in a lateral direction to allow removal of the compression molded article.
In the preferred embodiment of the present invention, the axial separating of the male and female mold halves is used with the cam mechanism to provide horizontal and/or rotary cam motions to laterally separate or disengage the molded article from the mold to allow axial removal of the molded article from the mold. The axial engagement of the male and female mold halves is used with the cam mechanism to provide the required rotary and/or horizontal motions to laterally close the mold.
The female mold half can be provided with a connecting plate which can move with the female mold and which has cam slots therein. A linkage is operatively connected to the male mold half and to the slide mold part and includes cam followers or travelers guided within the cam slots. Vertical reciprocation between the male and female mold halves moves the cam followers within the cam slots which causes forced lateral movement, via the linkage, of the slide mold part.
Alternatively, in another embodiment, the cam plate can be replaced by a tube having a spiral cam slot formed therein, and a rod with a radially extending cam follower can be guided within the tube for vertical and rotary movement. The rod is rotated by the cam follower which follows the spiral cam slots, as the rod is moved vertically within the tube. The rod can be connected to a swing lever which extends radially outwardly to be connected at a distal end to the slide mold part.
The embodiments of the invention provide a compression molding apparatus with the ability to produce a broader range of products with varying shape complexity and the utilization of a broader range of plastic materials.
The present invention is particularly suited for compression molded containers, and in particular container preforms, having externally threaded necks, the necks molded within the slide mold part. The slide mold part is separable into two parts. Horizontal separation of the two parts by the cam mechanism releases the molded neck from the slide mold part so that the neck can be axially (vertically) removed from the slide mold part, and the container removed from the molding apparatus. As will be recognized, the present invention can also be employed for molding tamper-evident plastic closures having pilfer bands connected by frangible bridges. Such bridges can be molded by use of the horizontally movable components of the present molding apparatus.
Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and embodiments thereof, from the claims, and from the accompanying drawings in which the details are fully and completely disclosed as part of the specification.